The present invention relates in general to blood perfusion systems for cardiac surgery, and, more specifically, to a waterless blood heater/cooler.
Heating and cooling devices are an important part of blood perfusion systems used during cardiac surgery. During surgery, blood is cooled in a bypass circuit to induce hypothermia to protect the organs. A separate cardioplegia circuit typically provides a dedicated flow of cooled solution directly to the heart, at least periodically. When the surgery has been completed, the blood and/or other fluids flowing in the two circuits are heated prior to the patient waking from anesthesia. During various circumstances that may arise during operation of the blood perfusion system, it becomes desirable not only to heat both circuits or cool both circuits simultaneously, but also to cool one circuit while the other is heating or to deactivate one circuit while the other is either heating or cooling.
Conduits carrying the blood and/or cardioplegia in each circuit pass through respective heat exchangers in order to perform heating or cooling in a controlled manner. Typical prior art systems use water or other heat exchange fluids passing through the heat exchangers thermally coupled to passages carrying the blood for adding heat to or removing heat from the blood/cardioplegia as necessary. An integrated heater/cooler unit having an integrated controller and an integrated power supply usually includes a single ice-bath compartment for selectably cooling the water in both water circuits and a pair of heating devices for selectably heating the water in the two circuits independently.
The size of a heat exchanger that is required is proportional to the efficiency of the heat exchange. Lower efficiency results in a larger heat exchanger and, consequently, a greater volume of blood is present within it. It is desirable to reduce the blood volume (priming volume) present within the perfusion system. Therefore, it would be desirable to increase the heating/cooling efficiency as well as improving temperature stability and reducing the cycle time when a new target temperature is commanded.
Prior art heater/coolers depending upon an ice bath for cooling require efforts to obtain the ice and to prepare the unit for operation. Once prepared, the heater/cooler unit must be used within a certain amount of time. Furthermore, the use of an ice bath and the pumps and conduits for carrying the heat exchange fluid are significant. The heater/cooler is usually contained within a separate cart, and space must be available in an operating room to accommodate it. Due to the large size of the equipment, it is not easily integrated with other operating room equipment. Thus, it would be desirable to reduce the size of equipment.
Heater used in previous blood heater/coolers are typically comprised of electrically resistive heating elements. A relatively high voltage has been required in order to provide the necessary heating characteristics. Because of the presence of the high voltage, safety measures to protect the patient and the users of the equipment must be taken which add expense to the equipment. Furthermore, the power requirements may exceed the available power from typical convenience outlets. Thus, it would be desirable to reduce the power requirements.
The use of purified water as a heat exchange fluid has associated maintenance requirements due to the potential for water induced corrosion and bacterial growth. The constant maintenance is costly and troublesome.